The invention relates to a method for environmentally benign paint spraying with a dispersion of oven-drying lacquer in water in a paint spraying station that is provided with a cubicle with water-rinsed rear wall for collecting and washing out of overspray in cubicle waste water, the entire cubicle waste water being separated by ultrafiltration into permeate and lacquer-containing residue, the entire permeate being returned to the paint spraying station, the lacquer-containing residue being enriched with lacquer by removing water until the lacquer content is essentially equal to that of dispersion that is fed to the paint spraying station the residue that is enriched with lacquer in this way being admixed to the freshly fed dispersion for reuse in spray painting, and with a constituent for preventing coalescence of the lacquer being admixed to the dispersion fed to the paint spraying station.
In prior art the overspray will be disposed of, which constitutes a heavy burden for the environment and is also very costly. For instance, a binding agent for oven-drying lacquer, which can be dispersed in water, is known from EP-0032554: the disposal of such a binding agent constitutes a heavy burden to the environment, because it Contains phosphor. Besides, special measures have to be taken so as to avoid conglutination of the appliances used for separating the overspray from the cubicle waste water, in this context cf. for example DE-3704683.
The separation of cubicle waste water into permeate and lacquer-containing residue by means of ultrafiltration is known, for example, from EP-0307047, EP-0245863, EP-0137877 or EP-0127685. On the other hand, it is known from EP-0318827 or EP-0271015 that the permeate has to be deacidified before it is returned to the paint spraying residue. Both of these aspects of the state of the art are taken into account in EP-0217212.
Experiments for the recuperation of the lacquer from the overspray in cubicle waste water are made reference to in "Oberflache +JOT" 5/1987, page 36, however, in this publication they are considered as "successful only in certain cases". In "Oberflache +JOT" 2/1988, pages 24-25, lacquer and binding agent circuits in the spraying cubicle are qualified as "future", while the recuperation of the lacquer by means of special reprocessing is mentioned as known. Also in DE-3800980, the recuperation of the lacquer by means of reprocessing is known.
In "Oberflache +JOT" 5/1988, pages 61-63, the use of amines for preventing coalescence of over-drying lacquer and the additional cleaning of the cubicle waste water by reverse osmosis following its separation into permeate and lacquer residue are mentioned. In this publication, the recuperation of the lacquer from the overspray is considered as being "in its initial stages of development".
Therefore it is in accordance with prior art that the lacquer-containing residue has to be disposed of.